Method for oxidizing an organic compound containing at least on c-c double bond

ABSTRACT

A process for oxidizing an organic compound having at least one C—C double bond or a mixture of two or more thereof comprises the following steps:  
     (I) preparing a hydroperoxide,  
     (II) reacting an organic compound having at least one C—C double bond or a mixture of two or more thereof with the hydroperoxide prepared in step (I) in the presence of a zeolite catalyst,  
     (III) regenerating the at least partially deactivated zeolite catalyst used in step (II), and  
     (IV) conducting the reaction of step (II) using a zeolite catalyst containing the catalyst regenerated in step (III).

[0001] The present invention relates to a process for oxidizing anorganic compound having at least one C—C double bond or a mixture of twoor more thereof by reacting the organic compound having at least one C—Cdouble bond or the mixture of two or more thereof with a hydroperoxidein the presence of a zeolite catalyst, regenerating this catalyst, andreusing the catalyst for the above-mentioned reaction following itsregeneration.

[0002] Processes for oxidizing an organic compound having at least oneC—C double bond, especially olefins, preferably propylene, using ahydroperoxide are known.

[0003] U.S. Pat. No. 5,374,747 discloses such an epoxidation processusing a titanium-coning molecular sieve having a structure which isisomorphous to zeolite 13, and the preparation of such a molecularsieve.

[0004] U.S. Pat. No. 5,384,418 discloses an integrated process forpreparing epoxides by reacting a hydroperoxide with an ethylenicallyunsaturated compound in the presence of a titanium silicalite.

[0005] Other processes for preparing epoxides in the presence of zeolitecatalysts are disclosed, inter alia, in U.S. Pat. No. 5,463,090 andEP-A-0 230 949, the first of which produces the hydrogen peroxide usedfor oxidizing from an anthraquinone process, whereas the latterdiscloses the epoxidation of propylene with hydrogen peroxide in thepresence of titanium silicalites defined therein.

[0006] According to U.S. Pat. No. 5,599,955, propylene, which is mostcommonly used for such oxidations, can be obtained starting fromsynthesis gas. U.S. Pat. No. 5,599,956 discloses a process for preparingpropylene oxide, wherein the propylene is obtained by steam cracking,catalytic cracking or catalytic dehydrogenation.

[0007] It is known that in these catalytic reactions organic depositsare formed after some time, which result in partial or completedeactivation of the catalysts, especially when using catalysts havingmicropores, for example zeolite catalysts such as titanium silicalite ortitanium-containing zeolite B.

[0008] These organic deposits can be mostly removed by calcining thecatalyst or washing with solvent (M. G. Clerici, G. Bellussi, U. Romano,J. Catal., 129 (1991), 159-167; JP-A-03 114536).

[0009] EP-A-0 743 094 discloses a process for regenerating aTi-containing molecular sieve by heating the molecular sieve at frommore than 150° C. to less than 400° C. This reference also disclosesthat it is possible to use the catalyst regenerated in this manner forreacting organic compounds, for example for the hydroxylation ofaromatic compounds, the ammoxidation of ketones, the oxidation ofsaturated hydrocarbons to obtain alcohols and ketones, and for olefinepoxidation. DE-A-44 25 672 discloses an oxidation catalyst based ontitanium or vanadium silicates having a zeolite structure and a processfor preparing epoxides from olefins, hydrogen and oxygen using thecatalyst described therein. It is also stated that the catalystdescribed therein may be regenerated.

[0010] Above-discussed U.S. Pat. No. 5,599,955 also mentions thepossible regeneration of the catalyst used in connection with theprocess described therein, but no details of the regeneration procedureare given.

[0011] As can be seen from the above, there is extensive prior artrelating to integrated processes for preparing epoxides, but the problemof practicable regeneration of the deactivated catalyst and the usefulintegration of such a step into the overall process remains unsolved.This step and its integration into the overall process are, however,critical for the economic viability of such a process. It is inprinciple possible to conduct regenerations as disclosed in EP-A-0 743094; these are, however, economically unviable because of the lowtemperatures used therein and the resulting long regeneration period.

[0012] It is an object of the present invention to provide a process foroxidizing an organic compound having at least one C—C double bond,regenerating the catalyst used in this process and reusing theregenerated catalyst for further reaction in the process.

[0013] We have found that this object is achieved by the process of theinvention.

[0014] The present invention accordingly provides a process foroxidizing an organic compound having at least one C—C double bond or amixture of two or more thereof, which comprises the following steps:

[0015] (I) preparing a hydroperoxide,

[0016] (II) reacting an organic compound having at least one C—C doublebond or a mixture of two or more thereof with the hydroperoxide preparedin step (I) in the presence of a zeolite catalyst,

[0017] (III) regenerating the at least partially deactivated zeolitecatalyst used in step (II), and

[0018] (IV) conducting the reaction of step (II) using a zeolitecatalyst comprising the catalyst regenerated in step (III).

[0019] Step (I)

[0020] This step relates to the preparation of a hydroperoxide. For thepurposes of the present invention, hydroperoxide refers to hydrogenperoxide as well as organic compounds of the formula R—O—OH, where R isalkyl cycloalkyl, aralkyl or aryl.

[0021] In the process of the invention, preference is given to usinghydrogen peroxide.

[0022] Processes for preparing the hydroperoxides are known and willherein only be recited briefly for the synthesis of hydrogen peroxide.

[0023] Hydrogen peroxide is preferably synthesized via an anthraquinoneprocess or directly from hydrogen and oxygen over noble metal catalysts.

[0024] In the anthraquinone process, a mixture is prepared which isreferred to as working solution hereinafter. This mixture comprises asolution of a 2-alkylanthraquinone, preferably 2-ethyl-, 2-butyl-,2-hexyl-, 2-hexenyl-, particularly preferably 2-ethylanthraquinone, in asolvent mixture comprising a quinone solvent and a hydroquinone solvent.The quinone solvent is generally selected from the group consisting ofaromatic and alkylaromatic solvents, preferably benzene, toluene,xylenes or higher alkylaromatics having 6 to 20, preferably 9 to 11,carbon atoms or mixtures of two or more thereof, such mixtures beingpreferred.

[0025] The hydroquinone solvent is generally selected from the groupconsisting of alkyl phosphates, alkyl phosphonates, nonyl alcohols,alkylcyclohexanol esters, N,N-dialkylcarbonylamides, tetraalkylurethanesor N-alkyl-2-pyrrolidone and mixtures of two or more thereof,tetrabutylurea being preferred.

[0026] The working solution is hydrogenated with hydrogen at from about20 to 100° C., preferably at from about 40 to 70° C., over acommercially available catalyst containing at least one transitionmetal, preferably from 0.5 to 20% by weight Pd on carbon, morepreferably from 2 to 15% by weight Pd on carbon. The catalyst can bearranged in the form of a suspension or a fixed bed.

[0027] The resulting hydroquinone-containing solution is oxidized withoxygen, preferably with air, more preferably with an oxygen- andnitrogen-containing mixture in which the oxygen is present indeficiency, based on the total mixture, in a suitable apparatus, forexample a bubble column. The oxidation is carried out at a reactiontemperature of from about 20 to about 100° C., preferably from about 35to about 60° C., until the hydrogen peroxide content of the solution isconstant and the conversion of the hydroquinone into quinone iscomplete.

[0028] The resulting hydrogen peroxide mixture is subsequently extractedwith a solvent which is not miscible with the solvent mixture,preferably with water, methanol, a monohydric alcohol having from 2 to 6carbon atoms or a mixture of two or more thereof, more preferably withwater. The resulting hydrogen peroxide mixture may then be used directlyin the reaction of step (II) of the process of the invention. Such awork-up procedure is disclosed, inter alia, in EP-B-0 549 013, whichsuggests using a mixture of water and an alcohol, preferably methanol.

[0029] Furthermore, the hydrogen peroxide preferably used for oxidationin the present invention may also be prepared directly from theelements. Processes for preparing hydrogen peroxide from the elementsoxygen and hydrogen are well known, as can be seen from DE-A-196 42 770and the prior art cited therein. In the process of the invention,hydrogen peroxide is preferably prepared from the elements according tothe process described in DE-A-196 42 770, which is incorporated hereinby reference in its entirety.

[0030] The essential aspects of the process described therein will nowbe recited briefly below.

[0031] According to the process described therein, hydrogen peroxide isprepared continuously by reacting hydrogen and oxygen in water and/orC₁-C₃-alkanols as reaction medium over a shaped catalyst body containingpalladium as the active component. This process yields a hydrogenperoxide solution having a hydrogen peroxide content of at least 2.5% byweight, based on the total solution.

[0032] Shaped catalyst bodies are catalysts in which the catalyticallyactive component is on the surface of specifically shaped carriers. Suchcarriers can be customary packing elements, for example Raschig rings,saddle bodies, Pall® rings, wire spirals or wire-mesh rings, which arecomposed of various materials suitable for coating with the activecomponent. Details of the above-mentioned carriers can be found inRömpp-Chemie-Lexikon, 9th ed., p. 1453f. The packing elements providedwith the catalytically active component are introduced into the reactorin the form of a loose bed. Preferred shaped bodies have channels withhydraulic radii (as defined in VDI-Wärmeatlas, chapter LE1) in the rangefrom 1 to 10 mm.

[0033] Preference is given to using shaped catalyst bodies which areinstalled in the reactor in the form of arranged packings and which havea large surface area for their volume, due to a multiplicity ofthroughflow channels. Such shaped bodies are known as catalystmonoliths. Suitable reactors for the preparation of hydrogen peroxideaccording to this process are described, for example, in EP-A-0 068 862,EP-A-0 201 614 and EP-A-0 448 884.

[0034] A further process for preparing hydrogen peroxide, which can alsobe integrated into the process of the invention as step (I), isdisclosed in WO 96/05138. This application is incorporated herein byreference in its entirety for the process for preparing hydrogenperoxide described therein and for the apparatus used for this purpose.

[0035] The process described therein involves introducing small bubblesof hydrogen and oxygen into a liquid stream of water and an inorganicacid in the presence of a catalyst comprising a metal of transitiongroup VIII of the Periodic Table. The liquid stream has a velocity of atleast about 3 m/s (10 feet/s) to create a continuous region of finelydispersed gas bubbles in a continuous liquid phase. As regards furtherdetails of this process for preparing hydrogen peroxide, reference ismade to the above-mentioned document.

[0036] The hydrogen peroxide used in the process of the invention canalso be prepared by contacting a secondary alcohol, for exampleα-methylbenzyl alcohol, isopropanol, 2-butanol or cyclohexanol withmolecular oxygen under conditions suitable for obtaining a mixturecomprising a secondary alcohol and hydrogen peroxide and/or a hydrogenperoxide precursor. Such a mixture typically comprises a ketonecorresponding to the secondary alcohol used in each case, i.e. a ketonehaving the same carbon skeleton as the secondary alcohol used, e.g.acetophenone, acetone or cyclohexanone, a small amount of water andvarying amounts of other active oxygen compounds, for example organichydroperoxides.

[0037] The hydrogen peroxide used can also be generated in situimmediately before or during the epoxidation, as described, for example,in EP-B-0 526 945, JP-A-4 352 771, EP-B-0 469 662 and Ferrini et al. in“Catalytic Oxidation of Alkanes using Titanium Silicate in the Presenceof in-situ Generated Hydrogen Ferroxide”, DGMK Conference on SelectiveOxidations in Petrochemistry, Sep. 16-18, 1992, p. 205-213.

[0038] Step (II)

[0039] This step of the process of the invention relates to the reactionof a compound having at least one C—C double bond or a mixture of two ormore thereof with the hydroperoxide prepared in step (I) in the presenceof a zeolite catalyst.

[0040] For the purposes of the present invention, “organic compoundhaving a C—C double bond” encompasses all organic compounds having atleast one C—C double bond. The compound in question may be a lowmolecular weight organic compound, i.e. a compound having a molecularweight of up to about 500, or a polymer, i.e. a compound having amolecular weight of more than 500. However, the process of the inventionis preferably used for low molecular weight organic compounds of thetype described above. These may be linear, branched or cyclic compoundswhich may contain aromatic, aliphatic, cycloaliphatic groups or acombination of two or more thereof. Preference is given to using anorganic compound having from 2 to 30 carbon atoms, more preferably from2 to 10 carbon atoms. The organic compound used is more preferably analiphatic monoolefin. However, it is also possible for the organiccompound used to have more than one ethylenically unsaturated doublebond, as is the case, for example, in dienes or trienes. The compoundmay contain additional functional groups, such as halogen, carboxyl, anester group, hydroxyl, an ether linkage, a sulfide linkage, carbonyl,cyano, nitro, amino or a combination of two or more thereof. The doublebond may be terminal or internal. It may also be part of a cyclicstructure, as is the case with cyclohexene. It is also possible to use amixture of two or more of these compounds.

[0041] Further examples of suitable organic compounds includeunsaturated fatty acids or derivatives thereof, such as esters andglycerides of such unsaturated fatty acids, and oligomers or polymers ofunsaturated organic compounds, such as polybutadiene.

[0042] Examples of such organic compounds include:

[0043] ethylene, propylene, 1-butene, cis- and trans-2-butene,isobutylene, butadiene, pentenes, isoprene, 1-hexene, 3-hexene,1-heptene, 1-octene, diisobutylene, 1-nonene, 1-decene, camphene,1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene,1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene,di-, tri- and tetramers of propylene, styrene and other vinylaromaticorganic compounds having at least one C—C double bond, diphenylethylene,polybutadiene, polyisoprene, cyclopentene, cyclohexene, cycloheptene,cyclooctene, cyclooctadiene, cyclododecene, cyclododecatriene,dicyclopentadiene, methylenecyclopropane, methylenecyclopentane,methylenecyclohexane, vinylcyclohexane, vinylcyclohexene, methallylketone, allyl chloride, allyl bromide, acrylic acid, methacrylic acid,crotonic acid, vinylacetic acid, crotyl chloride, methallyl chloride,dichlorobutenes, allyl alcohol, allyl carbonate, allyl acetate, alkylacrylates and methacrylates, diallyl maleate, diallyl phthalate,unsaturated triglycerides, for example soybean oil, unsaturated fattyacids e.g. oleic acid, linoleic acid, linolenic acid, ricinoleic acidand esters thereof including mono-, di- and triglyceride esters.

[0044] Mixtures of two or more such compounds, especially mixtures ofthe compounds exemplified above, can also be used.

[0045] Thus, the present invention particularly provides a process ofthe present type where the organic compound having at least one C—Cdouble bond is selected from the group consisting of a linear orbranched aliphatic olefin, a linear or branched aromatic olefin, alinear or branched cycloaliphatic olefin, each having up to 30 carbonatoms, and a mixture of two or more thereof.

[0046] The process of the invention is particularly useful for reactinglow molecular weight olefins, e.g. ethylene, propylene and the butenes,especially propylene.

[0047] Catalysts used in step (II) of the process of the invention aretransition metal-containing, microporous and/or mesoporous and/ormacroporous solids.

[0048] The oxidation of low molecular weight compounds in particular ispreferably carried out using transition metal-containing microporoussolids, particularly preferably zeolites containing transition metals,more preferably a zeolite-containing titanium, zirconium, chromium,niobium, iron or vanadium, and especially a titanium silicalite.

[0049] Zeolites are crystalline aluminosilicates having ordered channeland cage structures with micropores. For the purposes of the presentinvention, “micropores” corresponds to the definition given in “PureAppl. Chem.” 45, p. 71ff., particularly p. 79 (1976), and refers topores with a pore diameter of less than 2 nm. The network of suchzeolites is composed of SiO₄ and AlO₄ tetrahedra which are linked bycommon oxygen linkages. A review of the known structures may be found,for example, in W. M. Meier and D. H. Olson in “Atlas of ZeoliteStructure Types”, Elsevier, 4th ed., London 1996.

[0050] Furthermore, there are zeolites which contain no aluminum andhave Ti(IV) partly replacing Si(IV) in the silicate lattice. Titaniumzeolites, especially those having a crystal structure of the MFI type,and possible ways of preparing them are described, for example, inEP-A-0 311 983 or EP-A-0 405 978. Apart from silicon and titanium, suchmaterials may also contain further elements such as aluminum, zirconium,tin, iron, cobalt, nickel, gallium, boron or small amounts of fluorine.

[0051] The titanium in the zeolites described can be partly or whollyreplaced by vanadium, zirconium, chromium, niobium or iron. The molarratio of titanium and/or vanadium, zirconium, chromium, niobium or ironto the sum of silicon plus titanium and/or vanadium, zirconium,chromium, niobium or iron is usually in the range from 0.01:1 to 0.1:1.

[0052] Titanium zeolites having an MFI structure are known to beidentifiable from a particular pattern in their X-ray diffractiondiagrams and, in addition, from a skeletal vibration band in theinfrared (IR) at about 960 cm⁻¹, and thus differ from alkali metaltitanates or crystalline and amorphous TiO₂ phases.

[0053] Said titanium, zirconium, chromium, niobium, iron and vanadiumzeolites are usually prepared by reacting an aqueous mixture of an SiO₂source, of a titanium, zirconium, chromium, niobium, iron or vanadiumsource, e.g. titanium dioxide or an appropriate vanadium oxide,zirconium alcoxide, chromium oxide, niobium oxide or iron oxide, and ofa nitrogenous organic base template, e.g. tetrapropylammonium hydroxide,with or without added basic compounds, in a pressure vessel at elevatedtemperature for several hours or some days, resulting in a crystallineproduct. The crystalline product is filtered off, washed, dried andbaked at high temperature to remove the organic nitrogen base. In theresulting powder, the titanium or zirconium, chromium, niobium, ironand/or vanadium is present at least partly inside the zeolite frameworkin varying proportions in four-, five- or six-fold coordination. Toimprove the catalytic characteristics it is also possible to carry out asubsequent treatment by washing repeatedly with a solution of hydrogenperoxide containing sulfuric acid, after which the titanium orzirconium, chromium, niobum, iron, vanadium zeolite powder must be againdried and baked; this can be followed by a treatment with alkali metalcompounds in order to convert the zeolite from the H form into thecation form. The resulting titanium or zirconium, chromium, niobium,iron, vanadium zeolite powder is then processed into a shaped body asdescribed below.

[0054] Preferred zeolites are titanium, zirconium, chromium, niobium orvanadium zeolites, more preferred zeolites are those having a pentasilstructure, especially the types with X-ray assignment to a BEA, MOR,TON, MTW, FER, MFI, MEL, CHA, ERI, RHO, GIS, BOG, NON, EMT, HEU, KFI,FAU, DDR, MTT, RUT, LTL, MAZ, GME, NES, OFF, SGT, EUO, MFS, MCM-22 orMFI/MEL mixed structure. Zeolites of this type are described, forexample, in the above Meier and Olson reference. Also possible for thepresent invention are titanium-containing zeolites having the structureof UTD-1, CIT-1, CIT-5, ZSM-48, MCM-48, ZSM-12, ferrierite or β-zeoliteand of mordenite. Such zeolites are described, inter alia, in U.S. Pat.No. 5,430,000 and WO 94/29408, the relevant contents of which areincorporated herein by reference in their entirety.

[0055] Nor are there special restrictions in the pore structure of thecatalysts used according to the invention, i.e. the catalyst can havemicropores, mesopores, macropores, micro- and mesopores, micro- andmacropores or micro-, meso- and macropores, the definition of“mesopores” and “macropores” also corresponding to the definition givenin the Pure Appl. Chem. reference given above and referring to poreshaving a diameter of from >2 nm to about 50 nm or >about 50 nm,respectively.

[0056] The catalyst used according to the invention can also be amaterial based on a mesoporous oxide containing at least one transitionmetal and silicon or of a xerogel containing a transition metal andsilicon.

[0057] Particular preference is given to silicon-containing mesoporousoxides which additionally contain Ti, V, Zr, Sn, Cr, Nb or Fe,especially Ti, V, Zr, Cr, Nb or a mixture of two or more thereof.

[0058] If low molecular weight olefins such as, for example, propyleneare reacted in the present invention, particular preference is given tousing titanium-containing zeolite catalysts having exclusively orvirtually exclusively micropores such as, for example, titaniumsilicalite 1, titanium silicalite 2 or titanium-containing zeolite β,more preferably titanium silicalite 1 or titanium silicalite 2,especially titanium silicalite 1.

[0059] The use of a catalyst having particular mechanical stability ispreferred, if the reaction of step (II) is carried out as a fixed-bedprocess. Particularly suitable for this purpose are catalysts havingzeolite structure as described in DE-A-196 23 611, which is incorporatedherein by reference in its entirety with respect to the catalystsdescribed therein.

[0060] These catalysts are based on titanium or vanadium silicateshaving zeolite structure. As regards the zeolite structure, reference ismade to the above-mentioned preferred structures. These catalysts arecharacterized in that they have been shaped by strengthening shapingprocesses.

[0061] Suitable strengthening shaping processes which can be usedinclude in principle all strengthening shaping methods customarily usedfor catalysts. Preference is given to processes wherein shaping is doneby extruding in customary extruders, for example to obtain extrudateshaving a diameter of usually from 1 to 10 mm, especially from 2 to 5 mm.If binders and/or adjuvants are needed, extruding is advantageouslypreceded by a mixing or kneading procedure. Extrusion may be followed bya calcining step. The resulting extrudates are comminuted, if desired,preferably to obtain pellets or granules having a particle diameter offrom 0.5 to 5 mm, especially from 0.5 to 2 mm. Pellets, granules andalso shaped catalyst bodies formed in a different manner containvirtually no finer fractions than those having a minimum particlediameter of 0.5 mm.

[0062] In a preferred embodiment the shaped oxidation catalyst usedcontains up to 10% by weight of binder, based on the total mass of thecatalyst. Particularly preferred binder contents are from 0.1 to 7% byweight, especially from 1 to 15% by weight. Suitable binders are inprinciple all compounds used for this purpose; preference is given tocompounds, especially oxides, of silicon, aluminum, boron, phosphorus,zirconium and/or titanium. A binder of particular interest is silicondioxide, which may be introduced into the shaping step in the form ofsilica sol or tetraalkoxysilanes. Oxides of magnesium and beryllium andalso clays, e.g. montmorillonites, kaolins, bentonites, halloysites,dickites, nacrites and anauxites, can also be used as binders.

[0063] Adjuvants for the strengthening shaping processes include, forexample, extrusion adjuvants, a customary extrusion adjuvant beingmethylcellulose. Such adjuvants are usually burnt off completely in asubsequent calcining step.

[0064] The above-mentioned titanium and vanadium zeolites are typicallyprepared as described above in the general description of the zeolitecatalysts used according to the invention. The resulting titanium orvanadium zeolite powder is then shaped as described above.

[0065] It is also possible to regenerate oxidation catalysts based ontitanium or vanadium silicates having zeolite structure and containingfrom 0.01 to 30% by weight of one or more noble metals from the groupconsisting of ruthenium, rhodium, palladium, osmium, iridium, platinum,rhenium, gold and silver, which are also characterized in that they havebeen shaped by strengthening shaping processes. Such catalysts aredisclosed in DE-A-196 23 609, which is incorporated herein by referencein its entirety for the catalysts described therein.

[0066] What was said above in connection with DE-A-196 23 611 applieswith regard to the strengthening shaping processes, the binders and theadjuvants and the structure of the oxidation catalysts.

[0067] The catalyst disclosed in DE-A-196 23 609 contains from 0.01 to30% by weight, especially from 0.05 to 15% by weight, and in particularfrom 0.01 to 8% by weight, of the above-mentioned noble metals, in eachcase based on the amount of the titanium or vanadium zeolites.Particular preference is given to palladium. The noble metals can beapplied to the catalyst in the form of suitable noble metal components,for example in the form of water-soluble salts before, during or afterthe strengthening shaping step.

[0068] In many cases it is most advantageous, however, to apply thenoble metal components to the shaped catalyst bodies only after theshaping step, especially if a high temperature treatment of the noblemetal catalyst is undesirable. The noble metal components can be appliedto the shaped catalyst particularly by ion-exchange, impregnation orspraying. The application may be carried out using organic solvents,aqueous ammonia solutions or supercritical phases such as, for example,carbon dioxide.

[0069] It is quite possible to produce noble metal catalysts of varioustypes by means of the methods mentioned above. Thus, a type of coatedcatalyst can be produced by spraying the shaped catalyst bodies with thenoble metal solution. The thickness of this noble metal surface layercan be increased considerably by impregnating, whereas the catalystparticles are coated substantially uniformly with noble metal across thecross section of the shaped bodies in the case of ion-exchange.

[0070] In the process of the invention, greater preference is given tousing a zeolite catalyst obtainable by a process which comprises thefollowing steps:

[0071] (i) admixing a mix comprising a zeolite or a mix of two or morethereof with a mixture comprising at least one alcohol and water, and

[0072] (ii) kneading, shaping, drying and calcining of the admixture ofstep (i).

[0073] In step (i) of this catalyst preparation process, a zeoliticmaterial, preferably the zeolites described in more detail hereinbefore,in particular the titanium or vanadium zeolites described in more detailhereinabove, is processed with a mixture comprising at least one alcoholand water, a binder, optionally one or more organic viscosity enhancersand other prior art additives to obtain a plastically deformablematerial. This plastically deformable material obtained by intimatemixing, especially kneading, of the above-mentioned components is thenshaped, preferably by extrusion, and the resulting shaped body is driedand finally calcined.

[0074] The catalyst which is particularly preferably used according theinvention and its preparation may be more particularly described asfollows:

[0075] The zeolite used according to the invention is preferably atitanium-, zirconium-, chromium-, niobium-, iron- or vanadium-containingzeolite and especially a titanium silicalite, which in turn ispreferably a microporous titanium silicalite, more preferably amicroporous titanium silicalite having pentasil zeolite structure. Whatwas said in the general description of the zeolite used according to theinvention regarding the composition, structure, pore distribution andpreparation of the zeolites also applies here.

[0076] Suitable binders include in principle all compounds hitherto usedfor this purpose. Preference is given to compounds, especially oxides ofsilicon, aluminum, boron, phosphorus, zirconium and/or titanium. Abinder of particular interest is silicon dioxide which may be introducedinto the shaping step in the form of silica sol or tetraalkoxysilanes.Oxides of magnesium and beryllium and also clays, e.g. montmorillonites,kaolins, bentonites, halloysites, dickites, nacrites and ananxites, canalso be used as binders.

[0077] Preferred binders added in step (I) of the process of theinvention are, however, a metal acid ester or a mixture of two or morethereof. Particular examples of these are orthosilicates,tetraalkoxysilanes, tetraalkoxytitanates, trialkoxyaluminates,tetraalkoxyzirconates or a mixture of two or more thereof.

[0078] Particularly preferred binders are tetraalkoxysilanes. Specificexamples are tetramethoxysilane, tetraethoxysilane, tetrapropoxysilaneand tetrabutoxysilane, the corresponding tetraalkoxytitanium andtetraalkoxyzirconium compounds and trimethoxy-, triethoxy-, tripropoxy-,tributoxyaluminum, with tetramethoxysilane and tetraethoxysilane beingespecially preferred.

[0079] The catalyst which is particularly preferably used according tothe invention in the form of a shaped body contains preferably up toabout 80% by weight, more preferably from about 1 to about 50% byweight, especially from about 3 to about 30% by weight, of binder, ineach case based on the total mass of the shaped body, the binder contentbeing calculated on the basis of the amount of metal oxide formed.

[0080] The metal acid ester which is preferably used is used in such anamount that the resulting metal oxide content in the solid is from about1 to about 80% by weight, preferably from about 2 to about 50% byweight, especially from about 3 to about 30% by weight, in each casebased on the total mass of the shaped body.

[0081] As can already be seen from the above, mixtures of two or more ofthe above-mentioned binders can also be used.

[0082] It is essential to use a mixture containing at least one alcoholand water as pasting aid when preparing this shaped body. The alcoholcontent of this mixture is generally from about 1 to about 80% byweight, preferably from about 5 to about 70% by weight, in particularfrom about 10 to about 60% by weight, in each case based on the totalweight of the mixture.

[0083] The alcohol used is preferably the same as the alcohol componentof the metal acid ester preferably used as a binder, but the use ofanother alcohol is not critical either.

[0084] Any alcohol can be used, provided it is water-miscible.Accordingly, monoalcohols having from 1 to 4 carbon atoms andwater-miscible polyhydric alcohols can be used. Use is made inparticular of methanol, ethanol, propanol and n-, iso- and tert-butanoland mixtures of two or more thereof.

[0085] Usable organic viscosity enhancers likewise include all prior artsubstances suitable for this purpose. Preference is given to organic,especially hydrophilic, polymers such as cellulose, starch,polyacrylates, polymethacrylates, polyvinyl alcohol,polyvinylpyrrolidone, polyisobutene and polytetrahydrofuran. Thesesubstances promote primarily the formation of a plastically deformablematerial during the kneading, shaping and drying step by bridging theprimary particle and additionally ensure the mechanical stability of theshaped body during shaping and drying. These substances are removed fromthe shaped body during calcining.

[0086] Further additives that can be added are amines or aminelikecompounds such as tetraalkylammonium compounds or aminoalcohols andcarbonate-containing substances such as calcium carbonate. Such furtheradditives are disclosed in EP-A-0 389 041, EP-A-0 200 260 and in WO95/19222, the relevant contents of which are incorporated herein byreference in their entirety.

[0087] It is also possible to use acidic additives instead of basicadditives. Among other things, these acidic compounds can cause a fasterreaction of the metal acid ester with the porous oxidic material.Preference is given to organic acidic compounds which can be baked outby calcining after the shaping step. Carboxylic acids are particularlypreferred. It is also possible to include mixtures of two or more of theabove-mentioned additives.

[0088] The sequence in which the components of the material containingthe porous oxidic material are added is not critical. It is possible toadd the binder first, followed by the organic viscosity enhancer and theadditive, if used, and finally the mixture containing at least onealcohol and water, but also to change the sequence of binder, organicviscosity enhancer and additives.

[0089] Following the addition of the binder to the pulverulent porousoxide to which the organic viscosity enhancer may have been added, theusually still pulverulent material is homogenized in a kneader orextruder for 10 to 180 minutes. This is generally done at from about 10°C. to the boiling point of the pasting aid and at atmospheric pressureor slight superatmospheric pressure. Subsequently, the remainingcomponents are added, and the resulting mixture is kneaded until aplastically extrudable material has formed.

[0090] Kneading and shaping can in principle be carried out using any ofthe numerous customary prior art kneading and shaping apparatuses orprocesses generally used for the preparation of, for example, shapedcatalyst bodies.

[0091] As indicated above, preference is given to processes wherein theshaping is carried out as extrusion from customary extruders, forexample to form extrudates having a diameter of typically from about 1to about 10 mm, especially from about 2 to about 5 mm. Such extrudersare described, for example, in “Ullmanns Enzyklopädie der TechnischenChemie”, 4th edition, vol. 2, p. 295ff, 1972.

[0092] Following extrusion, the resulting shaped bodies are dried atfrom generally about 30° C. to about 140° C. (from 1 to 20 h,atmospheric pressure) and calcined at from about 400° C. to about 800°C. (from 3 to 10 h, atmospheric pressure).

[0093] It is possible to comminute the resulting extrudates. They arepreferably comminuted to obtain pellets or granules having a particlediameter of from 0.1 to 5 mm, especially from 0.5 to 2 mm.

[0094] These pellets or granules and also shaped particles formed in adifferent manner contain virtually no finer fractions than those havinga minimum particle diameter of about 0.1 mm.

[0095] Although there are no special limitations concerning theapparatus used for the reaction, step (II) of the process of theinvention is preferably carried out in a reactor battery which is packedwith one of the catalysts which can be used according to the invention,consisting of from two to seven, preferably from two to five, reactors,the catalyst being in the form of a tablet or an extrudate forming afixed bed or in the form of a powder forming a suspension. Examples ofusable reactor types that may be mentioned are stirred tank reactors andtubular reactors with or without external circulation.

[0096] In the reaction, a hydroperoxide-containing, preferably hydrogenperoxide-containing stream comprising an organic compound having atleast one C—C double bond, preferably a C₂-C₄-olefin, more preferablypropylene, is contacted with an organic solvent, preferably aC₁-C₆-alcohol, especially preferably methanol, and converted to thedesired oxidized compound, preferably to the epoxide, at from about 20°C. to about 120° C., preferably from about 30 to about 80° C. Thepreferred solvent methanol used can be fresh methanol or methanolrecycled from the epoxidation.

[0097] The ratio of the compound to be reacted to the hydroperoxide isnot critical and is in a molar ratio of from about 100:1 to about 1:10,preferably from about 1:1 to about 6:1.

[0098] The hydroperoxide content in the reactor (without compound to bereacted) is generally from about 0.1 to about 10%, the methanol contentis from about 10 to 90%, and the water content is from about 5 to about50%.

[0099] The amount of catalyst present in the reactor may also be variedwithin wide limits. The amount of catalyst present should be sufficientto complete the desired reaction within a short period of time. Theoptimum amount depends on many factors such as temperature, ratiobetween compound to be reacted and hydroperoxide, reactivity of thecompound to be reacted, reaction pressure, residence time, and flowrates of the compounds introduced into the reactor. The reactiontemperature is generally within the range from about 20° C. to about120° C., preferably from about 30° C. to about 100° C., more preferablyfrom about 30° C. to about 80° C. The temperature should generally bechosen so that the desired reaction can be carried out within aneconomically viable period of time. The residence time is generallywithin the range from about 10 min to about 24 h, preferably from about10 min to about 1 h, per reactor. The reaction pressure is generallychosen in the range from about 1 to about 100 bar, preferably from about15 to about 40 bar. The reaction mixture is preferably in liquid form.The reaction temperature, residence time and reaction pressure should beselected so that the hydroperoxide conversion is at least 50%,preferably at least 90%, in particular 99% or more.

[0100] After the reaction has ended, the oxidation product formed may beseparated from water, solvent and any byproducts. The separation may becarried out by all prior art separation methods, preference being givento distillative separation methods.

[0101] Any unconverted organic compound having at least one C—C doublebond and the solvent obtained can likewise be separated off and recycledto the reaction of step (II) if desired.

[0102] The reaction of step (II) may be carried out continuously,batchwise or part-continuously depending on the reactor used, forexample a fixed bed, a moving bed, a liquid bed or else as a suspensionprocedure in a stirred or unstirred manner. It is also possible to carryout the reaction in a one-phase or a multiphase system, as e.g. atwo-phase system. This reaction is preferably carried out as a fixed-bedprocess.

[0103] Once the epoxidation has progressed to a certain degree, thedesired oxidation product may be separated from the reaction mixture byany prior art separation method capable of separating the oxidationproduct from the reaction mixture. Preference is given to usingdistillative separation methods.

[0104] The resulting oxidation product is obtained essentially free fromthe catalyst used, especially when conducting the reaction as afixed-bed process, and may thus be worked up further without additionalcatalyst separation steps.

[0105] Unconverted starting material, i.e. the organic compound havingat least one C—C double bond or the mixture of two or more thereof andunconverted hydroperoxide, can be separated off and recycled in the samemanner or cracked to form products such as water or alcohol and oxygen,for example.

[0106] In certain embodiments of the present invention, especially whenpreparing the hydroperoxide starting from a secondary alcohol, in whichcase the hydroperoxide-containing mixture used for oxidation alsocontains a secondary alcohol or the corresponding ketone, the latter canin turn be converted to the secondary alcohol by a hydrogenation stepand recycled into the epoxidation of step (I). Hydrogenation reactionsof this type are well known in the art, and the hydrogenation ispreferably conducted over a transition metal catalyst containing, forexample, Raney nickel, ruthenium or palladium.

[0107] It is also possible to dehydrogenate the secondary alcohol, ifpresent, by known methods to obtain additional products of value such asstyrene, for example.

[0108] Step (III)

[0109] This step relates to the regeneration of the at least partiallydeactivated zeolite catalyst used in step (II).

[0110] The activity of the catalyst decreases with increasing reactiontime owing to increasing deposits which are mostly of organic origin.These deposits which are in particular organic, can be, inter alia,oligomers or polymers of the oxidation product formed, e.g. propyleneoxide. In the process of the present invention, the catalyst isregenerated if its activity falls below a certain threshold value. Thisthreshold value generally corresponds to an activity of 60% or less,preferably 40% or less, and especially 20% or less, in each case basedon the initial activity of the catalyst to be regenerated.

[0111] If the process of the invention is carried out in suspension,i.e. using a zeolite catalyst in the form of a powder, the catalyst maybe separated from the reaction mixture by customary solid/liquidseparation methods such as simple filtration, cross-flow filtration,centrifugation, etc. and regenerated. The regeneration is preferablycarried out by continuously separating and regenerating the catalystpresent in the reactor and recycling it into the reactor in regeneratedform.

[0112] If the zeolite catalyst in the reactor is packed as a fixed bed,the regeneration is advantageously conducted in the reactor itself, i.e.the catalyst is not removed but remains in the fixed bed in the reactorin a packed state.

[0113] To recover product of value present on the catalyst, the catalystmay further be washed with a solvent for the product of value obtainedafter the reaction of step (II) and before the regeneration of step(III). Solvents which can be used for washing include all solventscapable of dissolving the product of value which is desired in eachcase. Particular examples of solvents are water, alcohols, aldehydes,ketones, ethers, acids, esters, nitrites, hydrocarbons and mixtures oftwo or more thereof as discussed hereinafter in the discussion of thepreferred variation of regeneration in the present invention.

[0114] Generally, the catalyst is then heated in a stream of inert gaseither in the reactor or separately to effect regeneration. Oxygen isadded to the stream of inert gas once a certain temperature is reached.This temperature is generally from about 200 to about 800° C.,preferably from about 250 to 600° C., and more preferably from aboutmore than 400 to about 600° C. The amount of oxygen added to the inertgas is regulated in such a manner that the temperature duringregeneration, which temperature increases owing to the heat generated byburning off the mostly organic deposits, does not exceed about 800° C.,preferably about 600° C., more preferably about 550° C., and does notfall below about 400° C., preferably about 450° C., so that theregeneration proceeds sufficiently rapidly on the one hand andirreversible damage to the catalyst framework is avoided on the otherhand.

[0115] Following the complete removal of the deactivating, mostlyorganic deposits which is indicated by decreasing catalyst temperaturein spite of increasing oxygen content at the outlet of the regenerator,the catalyst is cooled down slowly, again under inert gas.

[0116] As indicated above, the regeneration of step (III) is carried outin an inert gas atmosphere containing oxygen or oxygen-supplyingsubstances. The term oxygen-supplying substance encompasses allsubstances which are capable of releasing oxygen or removingcarbonaceous residues under the indicated regeneration conditions. Theatmosphere is preferably a nitrogen-containing atmosphere comprisingoxygen or an oxygen-supplying substance. The oxygen-supplying substanceis preferably a nitrogen oxide of the formula N_(x)O_(y) where x and yare selected so that the nitrogen oxide is neutral, N₂O, anN₂O-containing waste gas stream produced by an adipic acid plant, NO,NO₂, ozone or a mixture of two or more thereof.

[0117] If CO₂ is used, the temperature is in the range from 500 to 800°C.

[0118] The oxygen content in the gas mixture used for regeneration ispreferably less than about 50% by volume, more preferably less thanabout 30% by volume, especially less than about 10% by volume, mostpreferably less than about 5% by volume.

[0119] In a further embodiment of the process of the invention, the gasstream may be moistened with steam or solvent vapor when the regeneratedcatalyst has cooled down to below about 200° C., preferably about 150°C., more preferably about 100° C. The solvents which may be used forthis purpose include the same solvents as may be used for washing the atleast partially deactivated catalyst before the actual regeneration.Preferred solvents are described hereinafter in more detail in thediscussion of the preferred regeneration of step (III) of the process ofthe invention.

[0120] After reaching the reaction temperature at which step (II) iscarried out and after sufficient solvent moistening, if performed, theregenerated catalyst is introduced into the reactor and the reactor ischarged with the solvent for the oxidation and reused for the reactionof step (II). If the catalyst remains in the reactor as a fixed bedduring regeneration, the reactor is filled with the solvent for theoxidation and the reaction of step (II) is carried out.

[0121] A preferred embodiment of the regeneration of an at leastpartially deactivated zeolite catalyst according to step (III) isdescribed in detail hereinafter.

[0122] In this embodiment, the regeneration comprises the followingsteps:

[0123] (a) heating an at least partially deactivated catalyst to 250°C.-600° C. in an atmosphere containing less than 2% by volume of oxygen,and

[0124] (b) subjecting the catalyst to a gas stream containing anoxygen-generating substance or oxygen or a mixture of two or morethereof in an amount in the range from 0.1 to 4% by volume at from 250to 800° C., preferably from 350 to 600° C.

[0125] This preferred regeneration preferably comprises a further step(c):

[0126] (c) subjecting the catalyst to a gas stream containing anoxygen-generating substance or oxygen or a mixture of two or morethereof in an amount in the range from 4 to 100% by volume at from 250to 800° C., preferably from 350 to 600° C.

[0127] The regeneration is conducted in essentially the same manner whenregenerating catalysts in the form of powders which have been used assuspension, when regenerating catalysts packed in a fixed bed in theform of a shaped particle, and when regenerating catalysts crystallizedon nets, for example stainless steel, Kanthal or packings, andsurface-coated catalysts consisting of an inert core comprising SiO₂,α-Al₂O₃, highly calcined TiO₂, steatite and an active catalyst surfacelayer comprising a zeolite, preferably a zeolite as defined above.

[0128] If the catalyst has been used in suspension, it must first beseparated from the reaction solution by a separation step, for examplefiltration or centrifugation. The resulting, at least partiallydeactivated pulverulent catalyst can then be regenerated. Using suchpulverulent catalysts, the steps carried out at elevated temperaturesduring the regeneration process are preferably conducted in rotary tubeovens. When regenerating a catalyst used in suspension, it is especiallypreferred to combine the suspension reaction and the regenerationprocess of the invention by continuously removing some of the at leastpartially deactivated catalyst from the reaction, externallyregenerating it using the process of the invention and recycling theregenerated catalyst into the suspension reaction.

[0129] As well as regenerating catalysts in the form of powders, it isalso possible to regenerate catalysts in the form of shaped bodies, forexample shaped bodies packed in a fixed bed. The regeneration of acatalyst packed in a fixed bed is preferably carried out in the reactoritself without the need to discharge or introduce the catalyst so thatit is not subjected to any additional mechanical stress. Theregeneration of the catalyst in the reactor itself involves stopping thereaction, removing any reaction mixture present, regenerating and thencontinuing the reaction.

[0130] According to step (a) the catalyst is heated to from about 250°C. to about 600° C., preferably about 400° C.-550° C., especially about450° C.-500° C., in an atmosphere containing less than 2% by volume,preferably less than 0.5% by volume, especially less than 0.2% byvolume, of oxygen, either in the reactor or in an external oven. Theheating of step (a) is preferably carried out at a heating rate of fromabout 0.1° C./min to about 20° C./min, preferably from about 0.3° C./minto about 15° C./min, especially 0.5° C./min-10° C./min.

[0131] In this heating phase, the catalyst is heated to a temperature atwhich the mostly organic deposits present begin to decompose while atthe same time the temperature is controlled via the oxygen content anddoes not increase so as to damage the catalyst structure.

[0132] Once the temperature range from about 250° C. to about 800° C.,preferably from about 350° C. to about 600° C., especially from about400° C. to about 600° C., which is desired for the decomposition of thedeposits, is reached, the catalyst may be left at these temperatures inthe atmosphere defined above if desired or if necessary owing to thepresence of a large amount of organic deposits.

[0133] In step (a) of the regeneration, if desired in combination withleaving the catalyst at the indicated temperature, the bulk of thedeposits is coked. This step involves the removal from the catalyst ofthe substances formed in this process, for example hydrogen, water,carbonaceous substances. The removal of the deposits by coking in thisstep reduces significantly the amount of energy generated during theburnoff of the catalyst in steps (b) and possibly (c) of the process ofthe invention by subjecting the catalyst to a gas stream containing moreoxygen, so that the slow heating of step (a) of the process of theinvention is in itself an essential step in the prevention of localoverheating of the catalyst.

[0134] In step (b) of this regeneration, the catalyst is then subjectedto a gas stream containing an oxygen-generating substance or oxygen or amixture of two or more thereof in an amount in the range from about 0.1to about 4% by volume, preferably from about 0.1 to about 3% by volume,more preferably from about 0.1 to about 2% by volume, at from about 250°C. to about 800° C., preferably from about 350° C. to about 600° C.

[0135] The amount of molecular oxygen or oxygen-supplying substancesadded is critical in that the amount of energy generated in this stepthrough burnoff of the coked organic deposits is accompanied by anincrease in catalyst temperature, so that the temperature in theregenerator must not depart from the desired temperature range fromabout 250° C. to about 800° C., preferably from about 350° C. to about600° C. The amount of molecular oxygen or oxygen-supplying substances ischosen in such a manner that the temperature in the apparatus is in therange from about 400° C. to about 500° C.

[0136] With increasing burnoff of the deposits the content of molecularoxygen or oxygen-supplying substances in the stream of inert gas must beincreased up to 100% by volume to maintain the temperature required forregeneration so that after completion of step (b) the catalyst issubjected, in step (c), to a gas stream containing an oxygen-supplyingsubstance or oxygen or a mixture of two or more thereof in an amount inthe range from more than about 4 to about 100% by volume, preferablyfrom more than about 3 to about 20% by volume, more preferably fromabout 2 to about 20% by volume, in the temperature range defined forstep (b).

[0137] A procedure is usually followed here in which the amount ofoxygen or oxygen-supplying substance in the feed gas stream iscontinuously increased as the temperature in step (b) decreases.

[0138] The temperature of the catalyst itself is maintained at atemperature range from about 250° C. to about 800° C., preferably fromabout 350° C. to about 600° C., especially from about 400° C. to about600° C., by appropriately controlling the oxygen content or the contentof oxygen-supplying substances in the gas stream.

[0139] The burnoff of the organic deposits is complete when thetemperature of the effluent gas stream at the reactor outlet decreasesin spite of increasing amounts of molecular oxygen or oxygen-supplyingsubstances in the gas stream. The duration of the treatment according tostep (b) and step (c), if necessary or desired, is generally from about1 to about 30 hours, preferably from about 2 to about 20 hours,especially from about 3 to about 10 hours, in each case.

[0140] The term “oxygen-supplying substances” is defined as above.

[0141] In another embodiment of the process of the invention the atleast partially deactivated catalyst is washed with a solvent to removeproduct of value still adhering to the catalyst prior to the heating ofstep (a). Washing is carried out in such a way that the products ofvalue adhering to the catalyst are each removable therefrom, but thetemperature and pressure are not sufficiently high to remove the mostlyorganic deposits as well. The catalyst is preferably merely rinsed witha suitable solvent.

[0142] Suitable solvents for this washing procedure include thus allsolvents in which the actual reaction product is readily soluble. Suchsolvents are preferably selected from the group consisting of water, analcohol, e.g. methanol, ethanol, 1-propanol, 2-propanol,2-methyl-2-propanol, 1-butanol, 2-butanol, allyl alcohol or ethyleneglycol, an aldehyde, e.g. acetaldehyde or propionaldehyde, a ketone,e.g. acetone, 2-butanone, 2-methyl-3-butanone, 2-pentanone, 3-pentanone,2-methyl-4-pentanone or cyclohexanone, an ether such as diethyl ether orTHF, an acid, e.g. formic acid, acetic acid or propionic acid, an ester,e.g. methyl formate, methyl acetate, ethyl acetate, butyl acetate orethyl propionate, a nitrile, e.g. acetonitrile, a hydrocarbon, e.g.propane, 1-butene, 2-butene, benzene, toluene, xylene, trimethylbenzene,dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane,1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane,1,1,1,2-tetrachloroethane, dibromoethane, allyl chloride orchlorobenzene, and mixtures of two or more thereof, if miscible.

[0143] Preference is given to solvents which already act as solvents inthe reaction, e.g. olefin epoxidation using the catalyst to beregenerated. Examples of such solvents for the epoxidation of olefinsare: water, alcohols, e.g. methanol, ethanol, 1-propanol, 2-propanol,2-methyl-2-propanol, 1-butanol, 2-butanol, allyl alcohol or ethyleneglycol or ketones, e.g. acetone, 2-butanone, 2-methyl-3-butanone,2-pentanone, 3-pentanone, 2-methyl-4-pentanone or cyclohexanone.

[0144] The amount of solvent used and the duration of the washingprocedure are not critical, but the amount of solvent and the durationof the washing procedure should be sufficient to remove the bulk of theproduct of value adhering to the catalyst. The washing procedure can becarried out at the temperature of the reaction or at highertemperatures, but the temperature should not be so high that the solventused for washing itself reacts with the product of value to be removed.If temperatures higher than the reaction temperature are used, a rangefrom 5° C. to 150° C. above the reaction temperature, in particular alsodepending on the boiling point of the solvents used, is generallysufficient. The washing procedure can be repeated more than once, ifnecessary. The washing procedure can be carried out under atmosphericpressure, under elevated pressure or even under supercritical pressure.Preference is given to atmospheric pressure or elevated pressure. If CO₂is used as solvent, preference is given to supercritical pressure.

[0145] If a pulverulent catalyst which has been used in suspension isregenerated, the removed catalyst is washed in an external reactor. Ifthe catalyst is packed in a reactor as a fixed bed, washing may becarried out in the reactor used for the reaction. In this case, thereactor containing the catalyst to be regenerated is rinsed one or moretimes with a solvent to recover residual product of value. Subsequently,the solvent is removed from the reactor.

[0146] The catalyst is generally dried on completion of the washingprocedure. The drying procedure is not critical per se, but the dryingtemperature should not too greatly exceed the boiling temperature of thesolvent used for washing to avoid abrupt evaporation of the solvent inthe pores, especially any micropores of the zeolite catalyst, since thiscan also damage the catalyst. In the regeneration of pulverulentcatalysts, drying is again carried out externally in a heating apparatusunder inert gas atmosphere. In the case of catalysts in a fixed bed, thecatalyst in the reactor is subjected to an inert gas stream at moderatetemperatures. It is possible, but not necessary, to dry the catalystcompletely. Pulverulent catalysts are usually dried until the powder isflowable. Nor is it necessary to dry fixed-bed catalysts completely.

[0147] In another embodiment of this regeneration, the regeneratedcatalyst obtained in step (c) is cooled down in an inert gas stream inan additional step (d). This inert gas stream may contain up to about20% by volume, preferably from about 0.5 to about 20% by volume, of avapor of a liquid selected from the group consisting of water, analcohol, an aldehyde, a ketone, an ether, an acid, an ester, a nitrile,a hydrocarbon as decribed above in the context of washing the catalyst,and a mixture of two or more thereof. Preference is given to usingwater, alcohol or a mixture of two or more thereof as vapor of a liquid.

[0148] As regards the preferably usable alcohols, aldehydes, ketones,ethers, acids, esters, nitrites or hydrocarbons, reference is made tothe corresponding discussion of the solvents which can be used in thewashing procedure of the process of the invention.

[0149] It is also important to cool down slowly when carrying out thecooling operation of step (d), since cooling down too fast (quenching)can adversely affect the mechanical strength of the catalyst. Themechanical properties of the catalyst can also be adversely affected byrapid rinsing of the regenerated, dry shaped catalyst bodies duringrestart of the reactor for further reaction. For this reason, it isadvisable to add the vapor of a liquid as defined above during thecooling phase. It is more preferable, however, not to add the vaporuntil the temperature is below a threshold temperature which is definedby the boiling point of the liquid used for the vapor. The thresholdtemperature is usually below about 250° C., preferably below about 200°C., especially below about 150° C.

[0150] After the regeneration the catalyst may be treated by basicand/or silylating compounds in order to remove acidic centers.Particularly suitable compounds are diluted aqueous solutions ofalkaline or alkaline earth hydroxides, alkaline or alkaline earthcarbonates, alkaline or alkaline earth hydroxy carbonates; Li, K, Naacetates and phosphates; and silylating esters, such as tetraalkoxysilane, tetraalkoxymonoalkyl silane and hexamethylene disilane.

[0151] Step (IV)

[0152] This step relates to reusing the catalyst regenerated accordingto step (III). To this end, the regenerated catalyst is recycled intothe reactor (if the at least partially deactivated catalyst has beenregenerated externally) and the reaction is carried out or continued asdescribed in step (II).

[0153] If the regeneration has been carried out in the reactor, thereaction is continued as described in step (II) on completion of theregeneration.

[0154] If, in the process of the invention, the organic compound havingat least one C—C double bond is selected from the group consisting of alinear or branched aliphatic olefin, a linear or branched aromaticolefin and a linear or branched cycloaliphatic olefin, each having up to30 carbon atoms, i.e. if an olefin is reacted with the hydroperoxide,this olefin can be obtained by dehydrogenating the correspondingsaturated organic compound to form the olefin and hydrogen.

[0155] Processes of this type for converting an alkane to thecorresponding olefin are known per se, in particular with respect topropane dehydrogenation. These processes are known in the literature asSTAR, CATOFIN® or OLEFLEX® processes and are described in detail, forexample, in Chem. Systems Report 91-5, 1992, p. 50ff., and also referredto in numerous patents, e.g. U.S. Pat. No. 4,665,267 or EP-A 0 328 507and U.S. Pat. No. 4,886,928.

[0156] These processes are characterized by an endothermic reactioncleaving the alkane to form the olefin, i.e. propane to propene, forexample, and hydrogen. Widely used catalysts are zinc and aluminumspinels doped with noble metals, chromium oxide/aluminum oxide, and alsosupported platinum catalysts.

[0157] Furthermore, promoted iron oxide catalysts for alkanedehydrogenations are known from DE-A 39 23 026.

[0158] The olefin which is preferably used as starting material, inparticular propylene, can also be obtained starting from thecorresponding saturated hydrocarbon by steam cracking, catalyticcracking. Such processes are described in more detail, inter alia, inU.S. Pat. Nos. 5,599,955 and 5,599,956 mentioned at the beginning, andin the prior art cited therein, both these references including theprior art cited therein being incorporated herein by reference in theirentirety.

[0159] In the process of the invention, especially when carried out asan integrated process, i.e. a process in which all volume streams areclosed loops, it is advantageous to obtain the olefin, especiallypropylene, to be used in the epoxidation step by dehydrogenating thecorresponding saturated organic compound, since the epoxidation steptolerates the unreacted alkane which is present in addition to theolefin and which comes from the dehydrogenation step and thus renders acostly alkane/olefin separation, especially a propane/propeneseparation, unnecessary.

[0160] The hydrogen from the alkane dehydrogenation can also be directlyused in the hydrogen peroxide formation, for example according to theanthraquinone process described at the beginning or the process startingfrom the elements as described at the beginning in the discussion ofstep (I) of the process of the invention.

[0161] The endothermic alkane dehydrogenation step can also be coupledwith the exothermic reaction of step (II) in an integrated heat andenergy system.

[0162] As indicated above, the process of the invention is particularlysuitable as an integrated process, i.e. a multistep process wherein thestreams of the various components used in the process are partially orcompletely closed loops, more preferably in combination with anappropriate integrated heat and energy system in which the amounts ofenergy generated in the exothermic process steps (II) and (III) can beused directly for running the endothermic step (1).

[0163] The Examples which follow illustrate the invention.

EXAMPLES Example 1

[0164] Synthesis of hydrogen peroxide by the Anthraquinone Process

[0165] 10 kg of a Pd on carbon hydrogenation catalyst (10% by weight ofpalladium) were added to 600 kg of a working solution consisting ofabout 10% by weight of 2-ethyl-anthraquinone dissolved in a mixture of70% by volume of Shellsol NF and 30% by volume of tetrabutylurea and themixture was contacted with hydrogen at 1.5-2 bar at 45° C. in a stirredtank until the theoretical hydrogen consumption had been reached. Thesolution which was now black was cooled to room temperature and thecatalyst separated off by filtration. The hydroquinone-containingsolution was oxidized with diluted air (10% by volume of oxygen, 90% byvolume of nitrogen) in three batches of 200 kg each in a jet tubereactor until the hydrogen peroxide content was constant. Following theoxidation, about 15 kg of DI water were added to 200 kg of the mixturewhich now contained about 1% by weight of hydrogen peroxide, and thismixture was stirred vigorously for 15 min. The aqueous phase was thenseparated off. This aqueous solution now containing about 9% by weightof hydrogen peroxide was stirred vigorously with the next 200 kg batchfor 15 min. Separation gave a mixture having a hydrogen peroxide contentof about 15% by weight which was used to extract the last 200 kg batchin the same manner. This procedure gave about 15 kg of an aqueoussolution containing about 20% by weight of hydrogen peroxide.

[0166] Better hydrogen peroxide yields may be obtained using acontinuous counterflow extraction, for example in a sieve-plate column,a pulsed sieve-plate column or a packed column.

Example 2

[0167] Synthesis of Hydrogen Peroxide According to DE-A 196 42 770

[0168] In the preparation of hydrogen peroxide according to theabove-mentioned application, the reaction vessel used was a 270 mlautoclave equipped with stirrer, thermostating and pressure regulationto 50 bar. This reactor was fitted with a catalyst monolith, centeredaround the stirrer axis so that the stirrer supplied the monolithuniformly with liquid and gas, prepared as follows. Feed lines foroxygen, hydrogen and the reaction medium were located in the base of thereactor. A discharge line from which the product/gas mixture could becontinuously discharged was located in the lid of the reactor. Aftersubtraction of the volumes of all internals an effective reaction volumeof 208 ml was available.

[0169] The catalyst monolith used was prepared as follows:

[0170] A corrugated net and a smooth net of V4A steel (1.4571, mesh size180 μm, wire diameter 146 μm) were placed on top of each other androlled up to give a cylindrical monolith 5 cm high and 5 cm in diameter.The ends of the nets were fixed by weld points. The distance between thethe ends of the smooth nets was at least 1 mm.

[0171] The monolithic support was treated in succession with acetone anddistilled water and then dried. The monolith was then treated with asolution of 25% by weight of concentrated hydrochloric acid and 75% byweight of distilled water at 60° C. for 10 min and rinsed with distilledwater. The treated monolith was placed in 150 ml of distilled water. 10drops of concentrated HNO₃ and 36 ml of a 1% strength by weight aqueoussolution of hypophosphoric acid and then 20 ml of a palladium-nitratesolution (1% by weight) were added. The mixture was heated first to 60°C. for 17 min and then to 80° C. for one hour. The mixture was thencooled and the catalyst monolith washed with distilled water and driedat 120° C. for 16 hours.

[0172] The reaction medium used for the preparation of hydrogen peroxideconsisted of methanol with 0.4% by weight of sulfuric acid, 0.1% byweight of phosphoric acid and 6 ppm of bromide (as sodium bromide)added. The reactor was flooded with the reaction medium. A stream of72.8 g/h of reaction medium, 48.6 l/h of oxygen and 5.5 l/h of hydrogen(gases referring to standard temperature and pressure) was then passedthrough the reactor. The product/gas mixture was continuously dischargedat the top of the reactor.

[0173] The conversion based on hydrogen was 76% (according to adetermination of the hydrogen content in the effluent gas) and theselectivity was 82%. The concentration of the resulting methanolichydrogen peroxide solution was 7% by weight (titration with 0.1 NKMnO₄).

Example 3

[0174] Epoxidation of Propene with Hydrogen Peroxide Over a Fixed-BedCatalyst

[0175] Flows of 27.5 g/h of hydrogen peroxide (20% by weight, obtainedas in Example 1), 65 g/h of methanol and 13.7 g/h of propylene werepassed through a reactor battery consisting of two reactors which had areaction volume of 190 ml each and which were packed with 10 g oftitanium silicalite-1 (TS-1) shaped into all-catalyst extrudates havinga diameter of 2 mm at a reaction temperature of 40° C. and a reactionpressure of 20 bar. The reaction mixture exited from the second reactorand was depressurized to atmospheric pressure in a Sambay evaporator.The removed low boilers were analyzed on-line by gas chromatography. Theliquid reaction effluent was collected, weighed and also analyzed by gaschromatography.

[0176] The hydrogen peroxide conversion decreased throughout the runningtime from initially 96% and reached 63% after 400 h. The selectivity,based on hydrogen peroxide, was 95%.

Example 4

[0177] Regeneration of Deactivated Catalyst

[0178] The deactivated fixed-bed catalyst of Example 3, which wascovered with organic products, was rinsed with methanol and then driedat 120° C. for five hours. 56 g of the dried shaped catalyst were placedin a rotary tube. First, the rotary tube was rotated very slowly (2 rph)and heated to 500° C. at 4° C./min under nitrogen (20 l/h). A gasmixture containing 9% by volume of oxygen and 91% by volume of nitrogenwas then fed into the rotary tube at 500° C. for 2 h. The volumepercentage of oxygen in the gas stream was then increased to 18% byvolume at 500° C. for 14 h while keeping the amount of gas constant (20l/h). The regenerated catalyst was then cooled under a steady stream ofgas. The weight loss was about 7%.

Example 5

[0179] Reuse of Regenerated Catalyst

[0180] Flows of 27.5 g/h of hydrogen peroxide (20% by weight, obtainedas in Example 1), 65 g/h of methanol and 13.7 g/h of propylene werepassed through a reactor battery consisting of two reactors which had areaction volume of 190 ml each and which were packed with 10 g of thecatalyst regenerated as described in Example 4 at a reaction temperatureof 40° C. and a reaction pressure of 20 bar. The reaction mixture exitedfrom the second reactor and was depressurized to atmospheric pressure ina Sambay evaporator. The separated low boilers we re analyzed on-line bygas chromatography. The liquid reaction effluent was collected, weighedand also analyzed by gas chromatography.

[0181] The hydrogen peroxide conversion decreased throughout the runningtime from initially 96% and reached 63% after 400 h. The selectivity,based on hydrogen peroxide, was 95%.

Example 6

[0182] Dehydrogenation of Propane to Obtain Propene

[0183] 210 ml of a dehydrogenation catalyst on the basis of chromiumoxide/Al₂O₃ in the form of 2 mm extrudates were placed in adouble-jacketed tube reactor (length 50 cm, internal diameter 35 mm).The reactor was heated to a wall temperature of 550° C. by means of asalt bath heat-transfer medium. Propane was passed over the reactoradmixed with nitrogen (volume ratio 20:80) from a steel cylinder at acontrolled pressure of 1.5 bar (LHSV=0.15/h). The effluent reactionmixture consisting of propane, propene and hydrogen was cooled to 30-40°C. and liquefied by compressing to about 35 bar to separate the C₃products from the hydrogen. This liquid gas mixture was usable in theepoxidation without further purification, since only the propylene wasreacted there and the propane was sufficiently inert.

[0184] Following epoxidation, unconverted C₃-propane/propene mixture wasdepressurized after testing for absence of peroxide and recycled intothe reactor for propane dehydrogenation.

[0185] After a reaction time of 3 h, the conversion of propane per passwas typically about 35%, the propene selectivity being 83 mol % (GCanalysis upstream of the compressor).

[0186] The deactivated catalyst was re-regenerable by adding air to thenitrogen carrier gas (max. 2% by volume of oxygen) after closing thepropane feed line.

Example 7

[0187] Direct Synthesis of Hydrogenperoxide in Water

[0188] The same catalyst as in Example 4 was used. The reaction mediumconsisted of water to which 0.4% by weight sulphuric acid, 0.1% byweight phosphoric acid and 6 ppm bromide (in the form of sodium bromide)were added. The reaction parameters were as follows: 268.0 g/h reactionmedium, 291.6 l/h oxygen, 32.4 l/h hydrogen, T=42° C. The conversionbased on hydrogen was obtained by a determination of the hydrogencontent of the spent gas and was 43% with a selectivity of 70%. Theconcentration of the obtained hydrogen peroxide solution was 5.6% byweight.

We claim:
 1. A process for oxidizing an organic compound having at leastone C—C double bond or a mixture of two or more thereof, which comprisesthe following steps: (I) preparing a hydroperoxide, (II) reacting anorganic compound having at least one C—C double bond or a mixture of twoor more thereof with the hydroperoxide prepared in step (I) in thepresence of a zeolite catalyst, (III) regenerating the at leastpartially deactivated zeolite catalyst used in step (II), and (IV)conducting the reaction of step (II) using a zeolite catalyst containingthe catalyst regenerated in step (III).
 2. A process as claimed in claim1, wherein the organic compound having at least one C—C double bond isselected from the group consisting of a linear or branched aliphaticolefin, a linear or branched aromatic olefin, a linear or branchedcycloaliphatic olefin, each having up to 30 carbon atoms, and a mixtureof two or more thereof.
 3. A process as claimed in claim 2, wherein theolefin is obtained by dehydrogenating the corresponding saturatedorganic compound to obtain the olefin and hydrogen.
 4. A process asclaimed in claim 3, wherein the dehydrogenation is carried out in thepresence of a heterogeneous catalyst containing at least one of thefollowing elements: Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re,Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, B, Al, Ga, C, Si, Ge andSn.
 5. A process as claimed in any of claims 1 to 4, wherein the zeolitecatalyst has micropores, mesopores, macropores, micro- and mesopores,micro- and macropores or micro-, meso- and macropores.
 6. A process asclaimed in any of claims 1 to 5, wherein the zeolite catalyst isselected from the group consisting of a silicate containing titanium,zirconium, vanadium, chromium or niobium and having MFI, BEA, MOR, TON,MTW, FER, CHA, ERI, RHO, GIS, BOG, NON, EMT, HEU, KFI, FAU, DDR, MTT,RUT, LTL, MAZ, GME, NES, OFF, SGT, EUO, MFS, MCM-22, MEL structure,MFI/MEL mixed structure and a mixture of two or more thereof.
 7. Aprocess as claimed in any of claims 1 to 6, wherein the zeolite catalystused is a catalyst obtainable by a process which comprises the followingsteps: (i) adding to a mixture comprising a zeolite or a mixture of twoor more thereof a mixture comprising at least one alcohol and water, and(ii) kneading, shaping, drying and calcining of the mixture of step (i).8. A process as claimed in any of claims 1 to 7, wherein the at leastpartially deactivated zeolite catalyst of step (III) is regenerated bythe following steps: (a) heating of an at least partially deactivatedcatalyst to 250° C.-600° C. in an atmosphere containing less than 2% byvolume of oxygen, and (b) subjecting the catalyst to a gas streamcontaining an oxygen-generating substance or oxygen or a mixture of twoor more thereof in an amount in the range from 0.1 to 4% by volume atfrom 250 to 800° C., preferably at from 350 to 600° C.
 9. A process asclaimed in any of claims 1 to 8, wherein the regeneration of step (III)of the at least partially deactivated catalyst is carried out in anapparatus for conducting the reaction of step (II) without removing thezeolite catalyst from this apparatus.